Reference to any prior art in this specification is not, and should not be taken as, an acknowledgment or any form of suggestion that this prior art forms part of the common general knowledge in any country.
Bibliographic details of references provided in the subject specification are listed at the end of the specification.
The cut-flower, ornamental and agricultural plant industries strive to develop new and different varieties of plants with features such as novel flower colors, better taste/flavor of fruits (e.g. grapes, apples, lemons, oranges) and berries (e.g. strawberries, blueberries), improved yield, longer life, more nutritious, novel colored seeds for use as proprietary tags, etc.
Furthermore, plant byproduct industries which utilize plant parts value novel products which have the potential to impart altered characteristics to their products (e.g. juices, wine) such as, appearance, style, taste, smell and texture.
In the cut flower and ornamental plant industries, an effective way to create such novel varieties is through the manipulation of flower color. Classical breeding techniques have been used with some success to produce a wide range of colors for almost all of the commercial varieties of flowers and/or plants available today. This approach has been limited, however, by the constraints of a particular species' gene pool and for this reason it is rare for a single species to have the full spectrum of colored varieties. For example, the development of novel colored varieties of plants or plant parts such as flowers, foliage and stems would offer a significant opportunity in both the cut flower and ornamental markets. In the cut flower or ornamental plant industry, the development of novel colored varieties of major flowering species such as rose, chrysanthemum, tulip, lily, carnation, gerbera, orchid, lisianthus, begonia, torenia, geranium, petunia, nierembergia, pelargonium, iris, impatiens and cyclamen would be of great interest. A more specific example would be the development of a blue rose for the cut flower market.
To date, creation of a “true” blue shade in cut flowers has proven to be extremely difficult. Success in creating colors in the “blue” range has provided a series of purple colored carnation flowers (see the website for Florigene Pty Ltd, Melbourne, Australia; and International Patent Application PCT/AU96/00296). These are now on the market in several countries around the world. There is a need, however, to generate altered flower colors in other species in addition to bluer colors in carnation and other cut flower species such as Rosa sp., Dianthus sp., Gerbera sp., Chrysanthemum sp., Dendranthema sp., lily, Gypsophila sp., Torenia sp., Petunia sp., orchid, Cymbidium sp., Dendrobium sp., Phalaenopsis sp., Cyclamen sp., Begonia sp., Iris sp., Alstroemeria sp., Anthurium sp., Catharanthus sp., Dracaena sp., Erica sp., Ficus sp., Freesia sp., Fuchsia sp., Geranium sp., Gladiolus sp., Helianthus sp., Hyacinth sp., Hypericum sp., Impatiens sp., Iris sp., Chamelaucium sp., Kalanchoe sp., Lisianthus sp., Lobelia sp., Narcissus sp., Nierembergia sp., Ornithoglaum sp., Osteospermum sp., Paeonia sp., Pelargonium sp., Plumbago sp., Primrose sp., Ruscus sp., Saintpaulia sp., Solidago sp., Spathiphyllum sp., Tulip sp., Verbena sp., Viola sp., Zantedeschia sp. etc. It is apparent that other plants have been recalcitrant to genetic manipulation of flower color due to certain physiological characteristics of the cells. One such physiological characteristics is vacuolar pH.
In all living cells, the pH of the cytoplasm is about neutral, whereas in the vacuoles and lysosomes an acidic environment is maintained. The H+-gradient across the vacuolar membrane is a driving force that enables various antiporters and symporters to transport compounds across the vacuolar membrane. The acidification of the vacuolar lumen is an active process. Physiological work indicated that two proton pumps, a vacuolar H+ pumping ATPase (vATPase) and a vacuolar pyrophosphatase (V-PPase), are involved in vacuolar acidification.
Vacuoles have many different functions and different types of vacuoles may perform these different functions.
The existence of different vacuoles also opens complementary questions about vacuole generation and control of the vacuolar content. The studies devoted to finding an answer to this question are complicated by the fact that isolation and evacuolation of cells (protoplast isolation and culture) induces stress that results in changes in the nature of the vacuolar environment and content.
Mutants in which the process of vacuolar genesis and/or the control of the internal vacuolar environment are affected are highly valuable to allow the study of these phenomena in intact cells in the original tissue. Mutants of this type are not well described in the literature. This has hampered research in this area.
Flower color is predominantly due to three types of pigment: flavonoids, carotenoids and betalains. Of the three, the flavonoids are the most common and contribute a range of colors from yellow to red to blue. The flavonoid pigments are secondary metabolites of the phenylpropanoid pathway. The biosynthetic pathway for the flavonoid pigments (flavonoid pathway) is well established, (Holton and Cornish, Plant Cell 7:1071-1083, 1995; Mol et al, Trends Plant Sci. 3: 212-217, 1998; Winkel-Shirley, Plant Physiol. 126:485-493, 2001a; Winkel-Shirley, Plant Physiol. 127:1399-1404, 2001b, Tanaka et al, Plant Cell, Tissue and Organ Culture 80 (1):1-24, 2005, Koes et al, Trends in Plant Science, May 2005).
The flavonoid molecules that make the major contribution to flower or fruit color are the anthocyanins, which are glycosylated derivatives of anthocyanidins. Anthocyanins are generally localized in the vacuole of the epidermal cells of petals or fruits or the vacuole of the sub epidermal cells of leaves. Anthocyanins can be further modified through the addition of glycosyl groups, acyl groups and methyl groups. The final visible color of a flower or fruit is generally a combination of a number of factors including the type of anthocyanin accumulating, modifications to the anthocyanidin molecule, co-pigmentation with other flavonoids such as flavonols and flavones, complexation with metal ions and the pH of the vacuole.
The vacuolar pH is a factor in anthocyanin stability and color. Although a neutral to alkaline pH generally yields bluer anthocyanidin colors, these molecules are less stable at this pH.
Vacuoles, occupy a large part of the plant cell volume and play a crucial role in the maintenance of cell homeostasis. In mature cells, these organelles can approach 90% of the total cell volume, can store a large variety of molecules (ions, organic acids, sugar, enzymes, storage proteins and different types of secondary metabolites) and serve as reservoirs of protons and other metabolically important ions. Different transporters on the membrane of the vacuoles regulate the accumulation of solutes in this compartment and drive the accumulation of water producing the turgor of the cell. These structurally simple organelles play a wide range of essential roles in the life of a plant and this requires their internal environment to be tightly regulated.
There is a need to be able to manipulate the pH in plant cells and organelles in order to generate desired flower colors.